1. Technical Field
The present invention relates to an exposure apparatus.
2. Related Art
Because of higher integration of electronic devices such as semiconductor integrated circuits, an exposure technique for forming minute patterns is demanded. Charged particle ray exposure excels in the minute processability (resolution) and pattern generating function, and in particular is used for example in manufacturing of a light exposure mask (drawing of a mask pattern) or trial manufacturing of cutting-edge devices. In the charged particle ray exposure, a sample is irradiated with a charged particle ray such as an electron ray or an ion beam to expose the sample to a device pattern of light (to draw the device pattern on the sample). In recent years, development of a multi-column technique for generating a plurality of charged particle rays in parallel has been moving ahead further, which is aimed at improving the throughput (for example, see Non-patent Literature 1).
Resolution of electron ray exposure as one example of charged particle ray exposure is restricted by scattering, in particular fogging, of an electron ray. Fogging of an electron ray is a phenomenon in which part (that is, electrons) of an electron ray that has been irradiated onto a sample surface is reflected thereon, and the reflected electrons fog a wide range of the sample surface as a result of the electrons being reflected again on a bottom portion and the like of an electron ray column that faces the sample surface. Not only the part of the electron ray that is reflected on a sample surface, but also secondary electrons that are generated due to the electron ray being scattered (inelastic scattering) in the sample may be scattered from the sample surface to fog the sample surface. For example, if the reflectance at a sample surface of an electron ray with acceleration voltage of 50 kV is approximately 20%, and the reflectance at a bottom portion of an electron ray column is 50%, approximately 10% of the electron ray fogs the sample surface.
In order to suppress fogging of an electron ray, a fog preventing mechanism is provided between an electron ray column and a sample (a stage that holds the sample). For example, Patent Literatures 1 and 2 disclose fog preventing mechanisms. In the fog preventing mechanisms, a plurality of metallic thin plates in which a plurality of openings is formed are overlapped one on another by aligning or slightly displacing the positions of the openings so that the plurality of opening become continuous in the direction of overlapping to constitute a plurality of holes. Also, Patent Literature 3 discloses a fog preventing mechanism in which a plurality of groove-like or slit-like holes are formed in a substrate made of silicon by anisotropic etching by using alkaline solution. In these fog preventing mechanisms, electrons having been guided to a plurality of holes are scattered repeatedly therein, and absorbed by a base material; therefore, scattering of an electron ray, that is, fogging onto a sample surface can be suppressed.    Patent Literature 1: Japanese Patent Application Publication No. H11-251223    Patent Literature 2: Japanese Patent Application Publication No. H11-54390    Patent Literature 3: Japanese Patent Application Publication No. H10-92370    Non-patent Literature 1: Proc. SPIE 7637, Alternative Lithographic Technologies II, 76370C (Mar. 10, 2010).
However, in electron ray exposure, in order to detect positional information of a sample, an alignment mark (also called a mark, simply) provided to a sample surface is irradiated with an electron ray, and electrons that are scattered from the sample surface are detected by using an electron detector that is disposed on the rear surface side (the electron ray column side) of a fog preventing mechanism. Accordingly, it is necessary, by means of a fog preventing mechanism, not only to suppress scattering of electrons and prevent fogging onto a sample surface, but also to guide electrons scattered from a sample surface to an electron detector. Also, due to a complex structure, low rigidity, or the like of fog preventing mechanisms that have so far been proposed, it has been difficult to produce and install a fog preventing mechanism for each electron ray column in an electron ray exposure apparatus that employs a multi-column technique.
An object of the present invention is to provide an exposure apparatus that comprises a fog preventing mechanism that guides at least a part of electrons that are scattered from a sample surface to an electron detector, and prevent an electron ray from fogging the sample surface.